As a result of active exploitation of the Daikoku deposits in the Chichibu Mine, much information was obtained on the structural features controlling the localization of the ore deposits.On the basis of this information, new ore deposits were researched both in the Akaiwa and the Doshinkubo sections. Geophysical prospecting and drilling were carried out effectively.
In consequence, in the lower horizon of the Akaiwa pit, a large massive ore deposit of replacement type was discovered in the Paleozoicc limestone. The ore consists mainly of sphalerite and pyrrhotite, with subordinate amounts of galena, chalcopyrite and magnetite.
In the Doshinkubo section, major iron ore deposit of contactmetasomatic origin occurs along the contact between limestone and quartz-diorite. The deposit is composed chiefly of magnetite, accompanied by some pyrite and locally concentrated chalcopyrite. Garnet skarn occurs in abundance in the footwall side of the deposit. Many large crystals of vesuvianite are contained in some parts of the skarn.

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The geological occurrences of ore shoots of the Oe ore deposits are controlled by many factors, such as difference in country rocks, pre-ore faults, mineralization-sequence, zonal arrangement of ore mine-rals according to depth, and supergerie enrichment.
Among those factors, faults and mineralization-sequence are most important. All veins of the Oe ore deposits are controlled by Senzaizawa faults which were formed before the mineralization, and occur only on the eastern side of those faults with the exception of the Senzai vein which extends to the western side.
The Oe ore deposits are made up of the repeated mineralization, and those ore minerals of repeated mineralization have different characters according to mineralization-sequence and occurrence, for example, the rhodochrosite at the later stage of mineralization gradually increases in Fe which depends on siderite morecule, and at the deep part of the ore deposits increases in quartz.
The sulfide ore minerals of the Oe ore deposits consist of pyrite, galena, sphalerite and small amount of chalcopyrite. Those sulfide ore minerals may be classified into two groups, sulfide (1) and sul-fide (2), by mineralization-sequence.
The sulfide (1) bears only Ag, while the sulfide (2) bears Ag and Au, and forms a large ore shoot at the eastern side of Senzai-Hisaki fault. All those special characteristics should be utilized not only in prospecting but also in mining, milling, as well as in the management of this mine.

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Recently, the Poronai formation (which develops) in the Kamiashibetsu district in the northeastern part of the Sorachi coal field has been correlated by some geologists with the upper-most part of the same formation in the Yubari coal field, on the basis of foraminiferal fossils.
But, the writers are inclined to believe that the former should be correlated with the lower part of the latter, according to the mega fossil assemblage and lithological features (examined).

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The geology of the so-called "Green Tuff" region is mainly composed of altered volcanic and pyroclastic rocks characterized by green colour and sedimentary rocks of Tertiary age. There are many ore deposits, such as Kuroko deposits and vein type deposits, in the region.
The breccia dikes are occasionally found in the ore deposits in some mines, namely, Itomuka, Jokoku, Ainai, Daichi, Furokura, Osarizawa, Takarakura, Hanaoka, Tatemata, Tsuchihata, Sachiu, Obori, Yaso, Ashio, Sawatari and Nakase, in this "Green Tuff" region. They are developed in close connect-ion with the ore bodies.
The results of field and microscopic observations reveal that breccias in the dikes consist of clay slate, black phyllite, chert and acidic plutonic basement rocks accompanied by various rocks of Tertiary formation, and phenocrystic crystals of quartz and small amounts of idiomorphic plagioclase, finegrained quartz, chlorite, epidote and a carbonate mineral occur in the matrix of breccia dikes.
The above fact suggests that the breccia dikes of this type are clearly of intrusive origin, and breccias of basement rocks were brought forth by the intrusion of acidic residual magma which abounds in volatile components.
The breccia dikes are divided into three groups by their formation stage as follows.
(1) Pre-metallization stage-in the Osarizawa and Ashio deposits.
(2) Interval between two metallization stages-in the Furokura, Takarakura and Nakase deposits.
(3) Post-metallization stage-in the Tatemata, Hanaoka and Kosaka deposits.
In the Sachiu and Daichi ore deposits two formation stage of breccia dikes, pre-and post-metallization stages, are discernible.
Some breccia dikes are reliable guides in ore prospecting, and seem to afford a clue for solving the problem of metallization stage in some deposits.

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